Current regulator tube



Oct. 19, 1943. c, c, MlNTER 2,332,392

CURRENT REGULATOR TUBE Filed Nov. 19, 1941 INVENTOR C C". M/A rf')?Aim/um ATTORNEY meme a. 19, 1943 UNITED STATES PATENT OFFICE" 2,332,392CURRENT REGULATOR TUBE Clarke 0. Minter, Em Orange, N. .1. ApplicationNovember 19, 1941, Serial No. 419,669 9 Claims. (01. 201-64) Thisinvention relates to the control oi. electrical current flowin in acircuit which includes a metallic electrical conductor of the firstclass, that is to say, a conductor formed of a metal or alloycharacterized by relatively high electrical conductivity, and which has,according to the accepted classification, a positive temperaturecoeilicient, so that an increase in the temperature of the conductoralways reduces its currentcarrying capacity under normal conditions.

The invention relates especially to a circuit in which a length of sucha conductor of the first class, in wire or filament form, is confined inan envelope with the space between the conductor and envelope occupiedby a confined gaseous atmosphere; and, more particularly, the inventionrelates to means for varying the current through a conductor soconfined, by control oi. variations in the thermal conductivity of theaforesaid gasare induced eous atmosphere, which variations by changes inthe ambient atmosphere and propagated through the envelope to theconfined gaseous atmosphere.

An object of the invention is to provide a controllable means foramplifying the normal efiect of ambient temperature on thecurrent-carrying capacity of such a conductor, so that it the nor-, maleffect of an increase in ambient temperature is to reduce thecurrent-carrying capacity of the conductor, one object is to produce inthe conductor, upon a given increase in ambient temperature, whethernatural or stimulated, a reduction in current-carrying capacity which isseveral times greater than has been predictable prior to the presentinvention.

An important advantage of such an increase in resistance and consequentdecrease in currentcarrying capacity will be readily apparent to thoseskilled in the art when it is realized that the aforesaid increase inresistance increases greatly the sensitivity to changes in ambienttemperature of any circuit in which the improved device of the presentinvention may be included;

- for example, a circuit provided with instruments for measuring orindicating changes in ambient temperature, one such application being tocircuits with instruments for supplying visible indications of changesin ambient temperature atfecting the conditions under which aeroplaneengines operate, especially during changes in altitude.

Furthermore, it is well known that the currentcarrying capacity 01' afew alloys is, for all practical purposes, independent or the ambienttemperature. Another class of substances, compris- Those skilled in theart will recognize without further elucidation that in all sorts ofelectrical circuits in which it is desirable to compensate, orneutralize, the positive coeificient of resistance of some essentialpart of the circuit, it would be of great advantage if a conductor ofthe first class could be endowed reliably with the ability to behavelike a conductor of the second class in the important respect that itwill exhibit a negative temperature coefiicient of resistance.

Accordingly, it is another object of the present invention to providefor so constructing and arranging a device of the class described,embodying a conductor of the first class, having normally a positivetemperature coeflicient of resistance, that an increase in ambienttemperature will produce in the conductor a predictable and measurabledecrease in resistance.

Ancillary to the last-named object, the following objects are amongthose realized by the present invention, viz.,

(1) To provide a novel means of reversing the normal effect of anincrease in ambient temperature on the current-carrying capacity of sucha conductor, so that, if the normal efiect of an increase in ambienttemperature is to reduce the current-carrying capacity of the conductor,per contra, the efiect will be to produce a desirable increase incurrent-carrying capacity.

(2) To provide for accomplishing the desired changes in current-carryingcapacity of such a conductor of the first class confined in an envelopecontaining a gaseous atmosphere surrounding the conductor, by meansadapted to eifect controlled changes in the thermal conductivity of thegaseous atmosphere, by changing the concentration of molecules in thespace surrounding the conductor, and thus to condition the conductorsuitably for the above recited purposes:

(a) By imparting to the conductor an exceptionally large positivetemperature coeflicient of resistance, much greaterthan normal; and,alternatively,

(b) By decreasing the resistance of the wire, and thereby to increasethe current-capacity thereof.

Other objects and features of the invention will become apparent tothose skilled in the art, as the description of the illustratedembodiment progresses.

In the accompanying drawing,

Fig. 1 is a view in longitudinal sectional elevation 01 an electricalresistance device in the construction of which the instant invention hasbeen embodied;

Fig. 2 is a similar view or" a modification of the device shown in Fig.1;

Fig. 3 is a similar view showing another modification; and

Fig. 4 is a similar view showing still another modification.

Referring now to the drawing in detail, the reference character 5designates in general a device which may be of the well known formexemplified by so-called ballast tubes, incandescent lamps, or othersuitable appliances, embodying an envelope or tube 5, preferably madeoi! glass or metal and confining a conductor 5 of the first class ashereinbefore defined, taking the form preferably of a wire or filamentsupported at each end by heavy metal leads 8 which are sealed suitablyinto the end walls of the envelope 6, the space 9 within the latter andsurrounding the conductor 1 being occupied by a gaseous atmosphere ID,the molecules H of which are conventionally indicated by stippling,without special regard to accuracy in proportions, the size of themolecules being exaggerated, while their number is, or course, of a muchreduced order for the sake of convenience in drafting.

If now the conductor I be energized by the imposition on its terminalsof a potential of suitable voltage, such as the usual commercialpotential, the conductor will be heated and its temperature will riseabove that of the surroundings. It will thereupon lose heat, principallyby conduction, through the gaseous atmosphere Ill to the walls of theenvelope 6, and thence to the surroundings.

If the temperature of the envelope 6 be regarded as the same as that ofthe ambient temperature, or only slightly above it, and alwaysproportional thereto, it has been shown theoretically that thedifference between the temperature of the wire 1 and the temperature ofthe wall of the envelope or tube 6 may be expressed accurately by thesubjoined known equation A,

in which Tw is the temperature of the wire (conductor), T: is thetemperature of the tub (envelope), I is the current through theconductor, R the resistance of the conductor, J is the mechanicalequivalent of heat, and K is a constant, while S is the thermalconductivity of the gaseous atmosphere l0 surrounding the conductor I.

Analysis of equation A shows that, if the power (1 R) dissipated in theconductor I remains constant, th difference between the temperature ofthe conductor I and that or the envelope i will vary with the thermalconductivity S of the gaseous atmosphere In, and by keeping thetemperature T: of the envelope 6 constant, if the thermal conductivity Sof the gaseous atmosphere I0 is decreased, the temperature Tw' of theconductor I will increase; while an increase in the thermal conductivityS of the gaseous atmosphere ID, on the other hand, will lower thetemperature Tw of the conductor I. Since the conductor I is of the firstclass and has a positive temperature coefficient of resistance, itsresistance will increase when the thermal conductivity S of the gaseousatmosphere I0 is decreased; and, for the same reason, he resistance orthe conductor I will decrease when the thermal conductivity S of theatmosphere I0 is increased.

The temperature Tr of the envelope 6 will, of course, vary in directproportion to changes in the ambient temperature, and the effect of anincrease in ambient temperature will be to decrease slightly, or notaffect at all, the temperatur Tw of the conductor I, and the resistanceof the conductor I.

This decrease in resistance of the conductor 1, accompanying an increasein ambient temperature, is not what would be expected normally from thepositive temperature coeilicient of resistance of the conductor, and thegreater decrease is due to the increase in thermal conductivity S of thegaseous atmosphere ID as the ambient temperature is increased, therebyacting to keep th temperature Tw of the conductor I practically constantas the temperature Tr of the envelope increases. It is to be noted that,according to the equation A, the product of is practically constant.

The properties and behavior toward changes in ambient temperature of aconductor enclosed in a gaseous atmosphere are well known, but have beendiscussed above in order to clarify the manner by which the procedure ofthe instant invention has been evolved in the novel development ofprinciples known in the art.

From equation A it can be seen that the thermal conductivity S of thegaseous atmosphere In plays a very important role in governing thetemperature Tw of the conductor, as th temperature of the envelope 6varies with the ambient temperature; and it will be realired by thoseskilled in the art that by the provision, according to the instantinvention, for causing the thermal conductivity S of the gaseousatmosphere to increase rapidly, and alternatively to decrease, in areliable and predictable manner, a useful and notable advance in the arthas been achieved. The manner in which provision has been made for suchcontrol will now be disclosed fully.

Taking first the problem of producing by an increase in ambienttemperature a decrease in the thermal conductivity S of the gaseousatmosphere III, instead of the normal increase in S produced by thepositive temperature coeflicient of thermal conductivity of the saidatmosphere 10, this result can be obtained byemploying the device shownin Fig. 2, which is preferably exactly the same in general structure asthat shown in Fig. 1, and like parts in each are accordingly identifiedby identical reference characters; but the envelope 6 in Fig. 2 containsalso a. volatile liquid H, the vapor molecules l3 of which will mix withthe molecules ll of the gas already present in the atmosphere I0.

It is clear that, owing to the increase in vapor pressure of the liquidas the ambient temperature increases, the concentration of vapormolecules l3 in the atmosphere ill will increase, and the thermalconductivity S of the atmosphere II) can be made to increase ordecreasawith an increase in ambient temperature merely by changing thenature and density of the atmosphere l0.

It the thermal conductivity S of the gas-vapor mixture l0|3 decreases asthe concentration by an" increase in ambient temperature, it will beseen of the vapor in the mixtureis increased from equation A that thedifierence between the temperature Tw of the conductor 1 and thattemperature T1; of the envelope 6 (or the ambient temperature)increases.v This means that the temperature Tw of the conductor 1increases faster than the ambient temperature, and the conductorexhibits an exceptionally large positive temperature coeificient ofresistance, much greater than normal.

A suitable mixture for the above purpose comprises hydrogen at apressure of approximately 10 mm. of mercury, the liquid [2 being anyvolatile liquid, such as water, alcohol, acetone, etc. As an example ofthe results obtained with such an envelope, I containing hydrogen andusing water as the liquid, I found by actual measurement that when theconductor I was made of nickel wire having a diameter'of .001, andcarried a current of 175 milliameters, the ambient temperature being C.,the resistance of the wire was 20.6 ohms.

At an ambient temperature of 295 C. the resistance of the wire whencarrying only 152 milliamperes was 30.5 ohms.

This increase in resistance is exceptionally large for'an increase inambient temperature of only 29.5 C. In fact, for nickel, with atemperature coefi'icient of .005 ohm C.- the increase should have beenonly 3 ohms.

If to the fully evacuated envelope a volatile liquid l2 such as water isadded, the following figures are cited from actual measurements to showthat under these conditions the wire 1, again nickel of .001" diameter,exhibits a negative temperature coefficient, in accordance with thepresent invention, and contrary to previous experience of other workersin this field.

For example, when conducting a current of 128 milliamperes, the wire hada resistance of 44.6 ohms when the ambient temperature was 0 C., butwhen the ambient temperature was increased to 28.5 C. and the wire wascarrying 134 milliamperes, its resistance was only 40.7 ohms.

Combinations of diiferent gases under varying pressures with a volatileliquid have been tried, the results obtained varying with the gas andliquid employed. Using gases varying in atomic weight from argon tomercury, it is possible to obtain a gaseous combination having positiveor negative temperature coefiicients of thermal conductivity of almostany desired degree, giving to a current-carrying conductor of the firstclass mounted in such an atmosphere an increasing or decreasingcurrent-carrying capacity as the ambient temperature is increased.

For purposes of obtaining a negative coefficient, a preferred embodimentof the present invention is that illustrated in Fig. 3, the generalstructural design of the device being the same as that shown in Fig. 1.There is also a small amount of volatile liquid [2 as shown in Fig. 2,but the atmosphere l4 surrounding the conductor 1 consists in thisinstance entirely of the vapor molecules [3 of the liquid l2. No fixedgas is used, the envelope 6 being pumped as free of air as possible. i

The effect of an increase in ambient temperature on the current-carryingcapacity of the conductor 1 in the Fig, 3 device is to enable theconductor 1 to carry more current at the higher temperature. This isreadily understood when 3 it is realized that as the ambient temperatureincreases, the vapor pressure of the volatile liquid l2 increases, and agreater number of vapor molecules l3 pass from the liquid I2 to theatmosphere I4 surrounding the conductor 1.

II the density of the vapor molecules l3 in the atmosphere I4 is keptbelow the point at which the thermal conductivity of the vapor moleculesbecomes independent of density, an increase in ambient temperature willproduce an increase in thermal conductivity of the atmosphere I4 byincreasing the concentration of vapor molecules l3, and thereby enablethe wire I to carry more current at the higher temperature. Any volatileliquid can be used and liquids varying in volatility from alcohols tomercury have given satisfactory results when so used.

A further modification of the invention, having as its purpose toprovide an increase in the thermal conductivity of the atmosphere l5urrounding the conductor 1, is illustrated in Fig. 4, the generalstructural disposition of the envelope 6 and contained conductor 1 beingpreferably as in Figs. 1 to 3.

In this modification the increase in the number of molecules in thegaseous atmosphere l5 as the ambient temperature increases is notproduced by a volatile liquid, as in the devices of Fig. 2 and Fig. 3,but is caused by the effect of an increasing ambient temperature on theadsorption or occulsion of a gas or vapor.

In the Fig. 4 device when the confined gas is hydrogen at a suitablepressure, a small quantity of activated material such as activatedplatinum, activated palladium, or a mixture of the two, or underfavorable circumstances of nickel or copper or other metal inproduction, is provided in the envelope as indicated at I6, and anincrease in ambient temperature will cause the activated material toliberate occluded hydrogen into the atmosphere I5, thereby increasingits thermal conductivity and the current-carrying capacity of theconductor 7.

In the Fig. 4 type of device the activated porous material I 6, whethermetallic or non-metallic,

may have adsorbed a gas or vapor, and as the ambient temperatureincreases, the porous material 5 will liberate gas or vapor into theatmosphere I 5, thereby increasing its thermal activity and thecurrent-carrying capacity of the conductor 1.

What is claimed:

1. An electrical resistance device comprising a sealed envelope having aunitary chamber, an electrical conductor of the first class confinedwithin, said unitary chamber, the space between said conductor and thewall of said unitary chamber containing a gaseous atmosphere havingsubstantially a given concentration, and a material within said unitarychamber for varying to a prescribed extent the concentration of saidgaseous atmosphere between the wall of said 3. An electrical resistancedevice comprising an electrical conductor of the first class suitablymounted in a sealed envelope having a unitary chamber, the space betweensaid conductor and the wall of said chamber containing vapor molecules01' a volatile liquid, and a small quantity of the said liquid adheringto the walls of the envelope.

4. An electrical resistance device comprising an electrical conductor ofthe first class in the form of a. wire suitably mounted in a sealedenveloped forming a unitary chamber, the space between the wire and thewall of the unitary chamber containing molecules of a fixed gas, andvapor molecules of a volatile liquid, and a small quantity of saidliquid adhering to the wall of said chamber.

' 5. An electrical resistance device comprising an electrical conductorof the first class suitably mounted in a sealed envelope forming a.unitary chamber, the space between the conductor and the chamber of thetube containing molecules of hydrogen, and a quantity of activatedpalladium or platinum or a mixture of the two suitably positioned on thewall of the envelope.

6. An electrical resistance device comprising an electrical conductor ofthe first class suitably 7. An electrical resistance device comprising asealed envelope forming a unitary chamber, an electrical conductorconfined within said unitary chamber having a positive temperaturecoefllcient acting normally to decrease the currentcarrying capacity ofthe conductor in response to increase in the ambient temperature, thespac between said conductor and the wall of sai unitary chambercontaining a gaseous atmosphere, and a material within said unitarychamber to reverse said normal decrease in currentcarrying capacity ofsaid conductor in response to increase in the ambient temperature andthereby to increase the current-carrying capacity of said conductor byincreasing the thermal conductivity of said gaseous atmosphere inresponse to said increase in ambient temperature.

8. An electrical resistance device comprising a sealed envelope forminga unitary chamber, an electrical conductor confined within said unitarychamber having a positive temperature coefllcient, the space betweensaid conductor and the wall of said unitary chamber containing a gaseousatmosphere, and a material within said unitary chamber to change thethermal conductivity of said atmosphere to cause the current-carryingcapacity of said conductor to be increased or decreased selectively inresponse to an increase in the ambient temperature.

9. An electrical resistance device comprising a sealed envelope having aunitary chamber, an electrical conductor of the first class confinedwithin said unitary chamber, and a heat conducting medium of a givenvolume in said unitary chamber and having a fixed concentration ofmolecules at a given temperature and operable to vary the concentrationof its molecules within said unitary chamber in response to changes inambient temperature to cause a variation in the current-carryingcapacity of said conductor.

CLARKE C. MINTER.

